CIRCUIT STAGE VAN HEURCK MICROSCOPE:

c. 1910

Maker: W. WATSON & SONS LTD.

Serial number: 11970

Click on a picture to see more
images and details.

DESCRIPTION

This compound microscope arises from an English tripod of the
form
used by Watson and similar to those used by Powell and Lealand and
others. It is black with lacquered brass button toes which are cork
shod. The limb is suspended by a trunnion joint with a rhodium or
chrome-plated tightening handle. The spread of the toes is just
slightly over 8 ½ inches, despite the Watson catalog quoted spread of 7
¾. The distance from the bottom of the stand to the axis of rotation of
the
limb is about 5 1/8
inches. Across the rear of
the tripod is a bar, a protrusion on top of which is where the limb
makes contact when the microscope is in the horizontal position. The
protruding piece also projects forward to make
contact with the limb in the vertical position. Thus there are stops
for the horizontal and vertical positions of the limb. It is signed on
the bottom of the rear toe with the serial number, and at the upper end
of the rear toe it is signed 'London'. The signature of 'W. Watson
& Sons Ltd is engraved on the upward
facing top curve of the 'Y'-shaped rear toe.

The gimbaled plane and concave mirrors are housed in a 2 ½
inch lacquered brass casing with knurled rings to hold the mirrors in
place. The mirror is supported by a black yoke attached to a a 1 ¼ inch
long stem, which is in turn, attached to a tubular fitting which slides
over the swinging tailpiece. The tailpiece swings on a brass screw
attached to a downward protruding piece of the stage.

The substage support, separate from the mirror tailpiece, is
fixed in
position and also comes down from the stage. The substage has coarse
focus by diagonal rack and spiral pinion. Fine substage focus is via a
knob protruding upward from the stage. This knob, unlike the main fine
focus knob, uncalibrated, but does have arrows showing the direction
the substage is moved; clockwise moves the substage down,
counterclockwise, up. There is a fixed ring for a
condenser which has controls for centering the condenser. Unlike later
models, the condenser housing does not swing out of the optical axis
and so the condenser must be removed from the housing if it is desired
to have the optical path below the stage without a condenser. A variety
of condensers are with the instrument. These include a
'Macroilluminator' for very low power work, especially during
photography, a 'Universal' Holos condenser, a 'Holoscopic Aplanatic Low
Power Condenser', a 'Holoscopic Oil Immersion Condenser,' a 'Holoscopic
Immersion Paraboloid, and a Substage Analyzer with Selenite cap with a
nosepiece Analyzer. For more details of these, please see the
accessories section below.

The Stage of this model protrudes further than in the No. 1
Van Heurck Model, and this allows full rotation of the 5 inch diameter
mechanical stage with its protruding controls. The rotation is not
calibrated, but the rotating edge is knurled. There is no easy
provision for centering the stage rotation, which, like the calibration
to the rotation was an extra. The mechanical stage has a one inch
horizontal range, and a 1 1/16
inch vertical range. The optional calibration for these stage movements
is a part of this instrument. These are calibrated 0-35 mm for the
horizontal movement and 0-40 for the vertical, with a vernier to read
tenths of a mm. The stage is controlled by two separate knurled knobs
controlling horizontal motion by worm screw and vertical by double
diagonal rack and spiral pinions. The optional stage bar with attached
clips slides on grooves on the edge of the square part of the stage top
plate. There is a knurled knob which can lock this bar in position.
There is a hole near the bottom into which this locking knob can be
screwed into. There are also two holes for the use of standard stage
clips.

The limb has a longer
arm than the No. 1 Van Heurck to allow it to
position the nosepiece in the center of the extended optical axis
necessitated by the full rotation of the stage. Coarse focus is by
diagonal rack and spiral pinion whilst the fine focus is via a long
lever controlled from the top edge of the rear part of the arm. The
knurled lacquered brass fine focus knob is calibrated and numbered from
0-10 with division increments of 0.1. It has arrows showing which
directions of rotation lowers and which raises the optical tube. There
is a steel pointer to
register these calibrations. The instrument has a black triple
nosepiece and it is signed with the Watson 'W' insignia. It is
inscribed on its upper surface 'revolve' with a curved arrow pointing
in the clockwise direction. Each of the three spots on the revolving
nosepiece has a label for a lens, these being 2/3,
1/6, and 1/12.
A variety of objectives are with the instrument and are described below
with the other accessories.

The outermost main optical tube is of 1.5 inch outside
diameter and is
about 5 inches long. There are two calibrated drawtubes, the outermost
and lower one being calibrated from 25 to 33 and also from 17 to 23 in
one tenth increments with the whole numbers labeled. The inner
drawtube is calibrated from 17 to 24 and is engraved similarly. The
lower drawtube has a three inch range whereas the upper inner drawtube
has a 3 ½ inch range. The inner draw tube accepts a 31 mm diameter
eyepiece, but there is also an adapter which allows the use of the
narrower 23 mm eyepieces. A variety of eyepieces are with the
instruments and are described in the accessory section of this web
page.

All the rack and pinion fittings have the capacity for
adjustment in
the event of wear, as do the the slides in which the tubes and substage
travel. Every part of this microscope works like it did over 110 years
ago. The black finishes are a gloss black and the lacquered brass a
mildly orange yellow. The black finishes of the stand probably have
been professionally redone in some years past. The signatures on the
foot, though readable, have no white coloring like most of the Watson
stands from this era do. The white lettering of the triple nosepiece
and the stage calibrations are intact.

The original case
is heavy and large with a top handle as well as two side handles. It
has dovetail joinery. There are two original accessory drawers, but no
original draw inserts remain. The original magnification card has
apparently been replaced with a typewritten
magnification chart.

ACCESSORIES FOR THE c. 1910 CIRCUIT STAGE VAN HEURCK MICROSCOPE:

Accessories for this microscope include two condensers, six objectives, polarizer with selenite cap, eyepiece analyzer, three eyepieces, a vertical illuminator, slides, compressor and livebox. There were also some Watson slides with it. The single condenser housing accepts both condensers.

Objectives currently with the instrument, all by Watson
except as noted are:

Achromatic 3 inch

Parachromatic 2 inch

Parachromatic 1 inch

Parachromatic 2/3
inch

Parachromatic 1/6
inch

Parachromatic 1/8
inch

Lietz 1/12oil immersion

Some readers may wonder how to compare these objectives to
modern
ones which are engraved as to magnification rather than focal length. A
table listing the available Watson objectives, their focal lengths,
n.a., and approximate magnification are provided on the Watson Objective Page.
That page also relates some of this information to mechanical tube
length. One should be aware that even now, as in the past,
magnification is not only a function of the eyepiece and objective, but
also the optics of ones own eyes; these differ from person to person so
magnification will differ slightly between individual users of the same
microscope. Put another way, even with a '10X' eyepiece and a '10X'
objective, the true magnification will almost never be exactly 100X.

A variety of condensers and other stage and substage apparatus were available at the time this instrument was produced.
The substage apparatus includes:

This later version of the 'Holoscopic Oil
Immersion Condenser',
is suitable for use with the highest power objectives and has an
immersion front which may be removed for use with dry objectives of
medium to high power. It is signed: 'HOLOS OIL IMM CONDENSER
5.5 mm n.a. 1.30
WATSON K5463'. This condenser housing fits the
microscope but has no signature and requires adapters for the optical
components; this condenser holder may not be by Watson.

In addition, there is also a polarizer to fit the substage with a
selenite
cap, along with a nosepiece analyzer, in addition to the a analyzer
fitting over the eyepieces (shown above with the eyepieces). This set
was also offered in the Watson
Catalogs, as was the analyzer fitting over the eyepieces.

Other accessories include
two vertical illuminators. One is the early
brass type with a coverslip used as the reflector. The other is
Watson's 'Combined Vertical Illuminator' set in a signed case,
providing the option of a tiny prism or coverslip for reflecting the
illuminating light beam. The Watson 'Combined Vertical Illumintor' was
first offered by Watson after 1921, and is shown in the
1923 catalog (thanks to Dr Joe Zeligs for this information).
Vertical illuminators are used for illumination of solid or opaque
objects with higher power objectives.
Although with low power, top-illumination from the side can suffice, as
the
magnification increases and the focal length shortens, light cannot
easily be directed onto the top of an opaque specimen. The vertical
illuminators allow the light to come down onto the specimen from above
through the objective, by reflecting incoming light off a coverslip at
an angle (in the simpler model), or via a tiny prism or mirror which at
the same time allows the reflected light to pass
back up in the opposite direction reaching the eyepiece. With the
coverslip type the reflected light goes up through the coverslip; with
the tiny prism, it is so small, light is able to pass up the
illuminator around it. These arrangements both have disadvantages and
many years later, more inventive and efficient methods of illuminating
opaque objects were developed. These included better vertical
illuminators and also directing light downward around the outside edge
of specially designed 'Epi' objectives. Examples of modern microscopes
providing this type of lighting are in this collection including a
Olympus Vanox with vertical illumination, and a Wild Epi-illumination
system.

HISTORY OF THE
EDINBURGH, VAN HEURCK, AND ROYAL MODEL MICROSCOPES

The
famous Belgian microscopist, Henri Van Heurck(1839-1909) was the
manager of his family business manufacturing paints and varnishes. He
became famous as a botanist, expert microscopist, photomicrographer,
and especially diatomist. More than one diatom species is named in his
honor. The basic plan for the Van Heurck stand was based on the earlier
Edinburgh stand, a model devised with the advice of an Edinburgh
professor. For more historical information about the various models of
the Edinburgh microscope see the Edinburgh
B page and the Edinburgh
H page.

Watson
& Sons had been making microscopes since about 1874. For some
time
in their early production, their microscopes were similar to other
contemporary makers, but soon they started to produce a variety of
interesting designs, including their own variation of the Walter
Bulloch Biological No. 2, and also a version loosely based on Wale's
New Working Microscope. In 1887, Dr Edington, a Lecturer in
Bacteriology from the University of Edinburgh suggested the first form
of the Edinburgh stand; according to Watson's delivery records, the
first example was sold on November 29, 1887. This stand was the
inspiration for the Van Heurck stand, and like the Van Heurck, started
out with a continental foot, but was soon ordered more often with a
tripod
foot. Like the Van Heurck, it was improved progressively over the
years. This culminated in the Edinburgh 'D' and 'H' models, (an example
of 'D' is shown to the left), which had most of the basic features of
the (later) 'Royal' model. In fact, when the Royal was first introduced, it was
actually slightly smaller than the Edinburgh H. The various Edinburgh
stands were at first indicated by the numbers 1,2,3, and 4, but by
1890, the letters A,B,C and D were used.

In
1889 or before, with all of his expertise, Van Heurck
suggested
the design of a microscope to his specifications, and this was the
first model of the Van Heurck microscope made by W. Watson and
Sons; the prototype was apparently delivered to Van Heurck in 1889*,
but there is no entry in the Watson delivery book for the prototype.
The first entry for a Van Heurck in the Delivery Books
was March of 1891. It was also
pictured in the first edition of Van Heurck's book also dated
1891.
This first version is identical to the 'Watson No. 4 Van Heurck Stand
A' seen in the 1893 catalog. Study of the illustrations shows that this
initial Van Heurck differed from the original Edinburgh mainly in two
features-the fine adjustment for the substage, and the ability to
rotate the mechanical stage. Van Heurck preferred to do all of his
photomicrography with a vertically oriented microscope which is why he
preferred his microscope to be made with a continental 'horseshoe' foot
and supported on a single pillar, so as not to interfere with substage
adjustments during the, (then) delicate operation, of photomicrography
with high power objectives. At the same time, many others preferred the
horizontal position for photography. For this reason, his stand was
also offered with the more stable English tripod foot which provided a
much more stable stand for photography in the horizontal position. Many
more examples with an English tripod exist than with the horseshoe
foot, as the tripod quickly became more popular.

*An
engraving of the Van Heurck 'A' stand
was used as a frontispiece to the introduction in the Ninth Watson
Catalog; the introduction in that catalog is dated 1889. I would like
to thank Allan Wisner for supplying me with this information.

As noted above, the Van Heurck instrument, as designed by the
diatomist, was at first provided on a continental foot with a single
pillar. Early examples had a standard one inch diameter main optical
tube, as pictured in the image in the preceding paragraph. In the 1893
catalog the 'No. 4 Van Heurck Stand A' had a 1 inch diameter main
optical tube with a single calibrated draw tube with tube length
variable from about 160 mm to 260 mm. The 'No. 4 Van Heurck Stand B,'
as shown to the left, had a double drawtube, the lower draw wider, (but
still only 1.5 inches in diameter), and controlled by rack and pinion.
In the 'B' stand the combined tube length could be varied from about
142 to 305 mm. It could be ordered as pictured with a continental foot,
or for a slightly higher price with a tripod foot. The Van Heurck was
apparently not yet considered the 'top of the line' instrument as No. 1
was the impressive 'Watson Swinging Substage Microscope,' No. 2 was the
'Scientist's,' and No 3. was the 'Research.'

In
1896, stand 'A' was no longer listed, but the usual Van Heurck was
still called the 'B.' Also in 1896, the 'Grand Model Van
Heurck
Microscope Stand' was first listed in the catalog. At that time it was
listed as identical to the B stand except for three
new features: 1)concentric controls for the mechanical stage (after
Terrell), 2)complete rotation of the stage, and 3)a
slightly larger foot with the Grand, the spread of the foot 'more than
ten inches'.

By 1898, the Edinburgh stand, which had been steadily
improved,
reached its final model in the 'H' but even the H continued to have
small improvements added over the years.

The
'Circuit Stage Van Heurck' was apparently first introduced about 1899
(as quoted in the Illustrated Annual of Microscopy for 1900). Like the
Grand Model, it had complete rotation to the stage, but was otherwise
identical to the smaller Van Heurck (now just called the Van Heurck
without a letter or number), including the stage controls. Later on,
the basic model simply became the 'No 1 Van Heurck'. Although listed in
the Watson 1900 catalog, the Circuit Stage Van Heurck was not
illustrated in that volume. The engraving to the left, from the 1902
catalog, illustrates the Circuit Stage Van Heurck with the optional
Watson-Males two speed fine adjustment. It should be noted that from
the start, the Terrell type stage could be ordered as an option for the
Circuit Stage Model, thus some might look like a 'Grand' but would be
distinguishable only by size.

To satisfy growing demand for a stand as perfect as the Van
Heurck but slightly smaller and therefore less costly, the 'Royal' model
was introduced about 1899-1900 as well. The major distinguishing
feature between this and the No 1 Van Heurck, was the inability to
rotate the mechanical stage (although some models with a rotating top
plate
are known); it was also of slightly smaller size than the Van Heurck,
and initially was even slightly smaller than the Edinburgh H stand. In
fact, it is a common misconception that the 'Royal' is generally a
larger stand than the 'Edinburgh H' and this is not true. The tripod
heights, arm/limb size, foot spread and stage are of identical size in
many examples; what makes the 'Royal' appear larger is the larger
diameter optical tube and drawtubes including the rack and pinion draw
tube. Without these differences and the fact that some 'Royals' have a
substage fine focus, the Edinburgh H and the 'Royal' could not be
differentiated from one another. This is confirmed by the examples in
my collection; the 'Royal'
and Edinburgh are virtually identical in size and differ mainly in the
diameter of main optical tube, the Royal's double draw tube, and fine
focus for the substage.

The Van Heurck microscope was offered with many options, and
some
of these options were to leave off certain standard features for a
discounted price. As noted above, it was eventually offered in three
different models: the 'No. 1', the 'Circuit stage' and the 'Grand.' At
any given time, the Grand was the largest. As noted above, the
introduction of the Grand preceded the 'Circuit Stage' Model by about
three years. These stands changed over the years and the 'Grand' Model
from early years was more like the Circuit Stage model of later years,
except for the size. Several features eventually distinguished the Van
Heurk microscopes from the Edinburgh H and the 'Royal'. The first was
a rotating mechanical
stage (not to be confused with ability of the top plate
of the stage to rotate, found on some other Watson stands as an option
including some Edinburgh models), and the second was the double
drawtubes, with the outer bottom one being adjustable by rack and pinion* .
Another feature found on these instruments (initially
standard,
later optional), was a fine focus for the substage, a feature found on
relatively few microscopes at the time. Van Heurck himself preferred
this to be controlled by a knob projecting vertically from the stage,
as seen in the example at the top of this web page, but another option,
quickly offered (and seen on the 'Royal'
model
in this collection), was to place the substage fine focus under the
stage projecting horizontally, just above the coarse substage focus
control. This below-the-stage version was apparently devised to satisfy
some critics who complained that the vertical control interfered with
stage access, but it was also slightly less expensive than the
vertically projecting version.

Eventually many features and option of the Van Heurck were
offered on the slightly smaller and less expensive Royal model.
The one feature that was never offered on the ' 'Royal' ' was the rotating
mechanical stage (although some models may have a rotating top plate,
the entire stage does not rotate as a unit as in the Van Heurck
models). Although the 'Royal' was almost otherwise the equal of the Van
Heurck,
it should not be referred to as a ' 'Royal' Van
Heurck' as Watson
clearly distinguished it from all the Van Heurck models and never
claimed it was a Van Heurk (see the discussion of this issue on the Royal Web Page.
In fact, Watson stated in their catalog that they produced the 'Royal'
because of so many requests to modify the Edinburgh stand
to include the features of the Van Heurck such as rack and pinion
drawtube and fine focus to the substage. So in fact, the 'Royal' , like
the Van Heurck was a derivative of the Edinburgh, but the 'Royal' started
as an Edinburgh, not as a Van Heurck. It would, in fact be more
appropriate to call it a ' Royal Edinburgh' as it is about the same size
as the Edinburgh H, differing mainly in the diameter of the main
optical tube and its double draw tubes. For a direct comparison of the
Edinburgh H and the Royal, see the Royal
and Edinburgh comparison Webpage on this site.

The Van Heurck was a work in progress and was continually
improved
and changed over the years. Early on, the main outer optical tube was
as small in diameter as others but it was gradually enlarged to
accommodate photography, initially one inch, then one and a half inches
in diameter and later, this became two inches in diameter; this
increase in tube diameter was also seen on the later versions of the
'Royal' microscope. The size of
the foot changed many times over the years as well. The condenser
housing on the model shown on this page could not be swung out of the
optical axis, but that feature was added later, not only to the Van
Heurk models but also to the 'Royal' and the Edinburgh too. Initially the
mirror was on a swinging support, but this was abandoned in later
models.

As more improvements were made, many were offered as options.
It is
a common misconception that the 'Grand' Model had more features by
nature, but in reality, as time went on, all the Van Heurk microscopes
had almost all the same optional features, except as noted below. These
option included calibrated verniers for the stage X and Y motions
(found on the example here), graduated rotation to the stage, rack and
pinion stage rotation, adjustable centering of the stage, locking for
the stage position, and rotation to the substage. A two speed
Males-Watson fine focus was eventually an option on the Van Heurck with
separate adjustment wheels for each speed; this option could be ordered
on most other Watson microscopes at that time; see the Holos Fram, for
example. Another option was the
location of the substage fine focus as noted above; eventually the very
presence of the substage fine focus was an option.

The main permanent differences between the three models of Van Heurcks were
the ability to fully
rotate the stage on the Circuit stage and Grand Models (but not on the
the No. 1 where the stage could rotate, but not 360 degrees), the concentric
mechanical stage controls for the Grand (but also available as an
option for the Circuit Stage Model, starting in 1900), and the size of
each stand, the Grand being the largest, the No 1. and the Circuit stage being smaller.
Because of all the possible combinations of options, and also because
their size changed over the years, few Van Heurck Models are exactly
alike. A chronology of these developments follows, and a comparison of
some of the features of these microscopes is noted in the table below.

CHRONOLOGY OF EVENTS IN THE DEVELOPMENT OF THE EDINBURGH,
ROYAL, AND VAN HEURCK SERIES OF MICROSCOPES:

1874-: Watson starts to produce microscopes.

1874-1887: Watson produces microscopes of the
usual designs but
eventually makes their own version of other famous stands including
those of the American makers, Bulloch and Wale.

1887: The first Edinburgh microscope is sold,
based on suggestions by Dr. Edington of Edinburgh.

1889:
The first Van Heurck microscope, apparently a prototype is pictured as
the frontispiece of the Watson 1889 catalog, but not listed. The
engraving is identical to the engraving in the 1893 catalog for the Van
Heurck 'A' Stand.

1891: The first entry in the Watson Delivery Books of a Van Heurck microscope,
being based on the Edinburgh stand. It had a 'horseshoe' foot.

1893: The Watson Catalog offered the No. 4 Van
Heurck microscope in
two versions both with a horseshoe foot; Stand 'A' had only a single
drawtube and did not have a
rack and pinion adjustment to the drawtube. Stand B had a larger
diameter main optical tube with two drawtubes, the lower one adjustable
by rack and pinion. Either version could be obtained with a tripod foot
as an option for additional cost.

1895: The 'Grand Van Heurck' is first offered, and
is seen in the 1896 catalog with the new
features being complete rotation to the stage, the concentric controls
for the mechanical stage, and the slightly larger size of the stand.
The Van Heurck 'B' is offered but the 'A' with single drawtube is no
longer mentioned. The grand is 7/8 inch taller than the 'B.'

1900: The 'Circuit Stage' Van Heurck Model is introduced.
It has the
complete rotation of the stage but is otherwise identical to the 'B'
stand.

1900: The 'Royal' is also introduced,
smaller than the
Van Heurck models, but with options for almost all the same features
except for stage rotation; the 'Royal' was never offered with stage
rotation. It is initially slightly smaller
than the
Edinburgh 'H' model! Standard features included the double
drawtube
with rack and pinion adjustment to the lower one. Initially,
substage fine adjustment was standard on the 'Royal' but located under
the stage near the substage coarse adjustment. Later this became optional.

*-It
becomes even more
confusing, because eventually, even the rack and pinion adjustment for
the drawtube could be ordered as an option on 'lower class' microscopes
such as the Edinburgh stand.

OPTIONS FOR THE MICROSCOPES:
The following table lists
options (including optional deletions) for the Edinburgh, Royal and Van
Heurck Models. It may be incomplete, as the author has not had access
to every single Watson catalog relevent to the period.

VAN
HEURCK NO. 4, 'A' MODEL

DATES

STANDARD
FEATURES

OPTIONAL
FEATURES

1893

Horseshoe foot, single draw,
Mechanical Stage
with separate controls for horizontal and vertical motion which rotates
but not a full 360 degrees, Substage Fine Adjustment,
Projecting
upwards in back of stage, clamping lever for inclination Joint.
The mechanical draw-tube length can vary from 160
to 260
mm.

Double Draw, with one Mechanical
Draw tube, otherwise
same as 'A' but with the extra draw-tube , the mechanical
tube
length has a longer range of from 142 to 310 mm.

Tripod Foot, Binocular Body

1896

Tripod Foot now standard,
otherwise same as 1893

same as 1893, except now the
Horseshoe foot was optional

VAN
HEURCK NO. 1

DATES

STANDARD
FEATURES

OPTIONAL
FEATURES

1900

Same as Van Heurck B of 1896

Same as 1896 with
additional option of Strnger's fine adjustment

1902

same

Same but also the Males-Watson
fine adjustment and
the Spindle head fine adjustment AND hinged substage which can be
turned aside out of the optical axis

1906

same

same

1912

same except now the substage fine
adjustment is an option

Choice of above or below stage
substage fine adjustment

1918

same
except now all Van Heurcks have hinged substage standard, which allows
the substage to be turned aside and out of the optical axis

same as 1912

1921

same as 1912, but now the
substage bar extension sliding on dovetail to allow
greater range of accessories of different heights as was previously
only offered for the Grand, then the Circuit stage, is now offered for
all VanHeurcks

1923

VAN
HEURCK CIRCUIT STAGE MODEL

DATES

STANDARD
FEATURES

OPTIONAL
FEATURES

1900

Identical to No. 1 but with
complete stage rotation

Identical to No. 1

1906

Same as 1900

Same as 1900

1912

same except now the substage fine
adjustment is an option

Choice of above or below stage
control of substage fine adjustment

1918

same
except now all Van Heurcks have hinged substage standard, which allows
the substage to be turned aside and out of the optical axis

same as 1912, but now the substage
bar extension
sliding on dovetail to allow greater range of accessories of different
heights as was previously only offered for the Grand

1921

same as 1918

same as 1918

1923

----

----

VAN
HEURCK GRAND MODEL

DATES

STANDARD
FEATURES

OPTIONAL
FEATURES

1896

Identical to the Van Heurck 'B'
Stand, with the
addition of concentric controls for the mechanical stage, and extension
of the stage and arm forward to allow complete
stage rotation and larger overall size.

Identical to Van Heurck 'B' model.

1900

Identical to Circuit stage Model,
but larger

Identical to Circuit stage model
but optionally the same stage as the No. 1 instead of fully rotating,
reduced the price by
3 pounds.

1902

Identical to Circuit stage Model,
but larger

Identical to Circuit stage model
but optionally the
same stage as the No. 1 instead of concentric controls, reduced the
price by 3 pounds. Also option of Stringer's fine
adjustment, or
Males-Watson Two speed fine adjustment, or Spindle Milled-head fine
adjustment, all at extra cost.
Optional hinged substage so it can be swung out of the
optical axis.
Also a substage bar extension sliding on dovetail to allow greater
range of accessories of different heights.

1906

Identical to 1902

Same as 1902 but also offered the
Scop Mechanical
Stage instead of the usual circuit stage, price the same as the
standard model.

1912

same

same as 1906

1918

same
except now all Van Heurcks have hinged substage standard, which allows
the substage to be turned aside and out of the optical axis

1921

Same

Side Limb or Horizonatal fine
adjustment for same price.

The author would like to thank Dr Joe Zeligs and Allan Wisner for help, references and advice on this page.